No doubt that is a hot price. The going rate for one of those in that represented condition is about 7-9k.

I would hold off on the trans computer until you know for a fact that it is bad. How did you determine the transmission actually downshifted, or did you just observe an rpm spike at the moment of failure?

I still maintain that the transmission controller and the engine controller talk to each other and will not allow a downshift that would kill the engine. Failing that I have to think that if somehow it did get in that situation it would have tried to save the engine by cutting the fuel supply by releasing the IP rack to minimum.

I still think you have a runaway condition caused by the engine consuming its own lube oil based on earlier statements.

Not trying to be difficult but just making sure you really get to the root cause of the problem without just throwing parts at it.

The TCM will have to be recoded to match the car, with Star DAS, it's not just a plug and play operation. I suspect this will be several hundred dollars for the part and north of a hundred to pay shop labor to do the recode.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech